1. Field of the Invention
The present invention relates to an input device including a flat-type input unit capable of detecting a position where a control object has approached on the basis of changes in an electrostatic field between electrodes, and a switch unit for producing an ON/OFF output signal.
2. Description of the Related Art
For a personal computer, as an input device used to input coordinate data for moving a cursor displayed on a screen, there is an input device, other than an input device called a mouse, called a flat-type input device that utilizes changes in capacitance.
In such a flat-type input device, a plurality of X electrodes face a plurality of Y electrodes, and an insulating layer is provided between the X electrodes and the Y electrodes. The X electrodes and the Y electrodes are arranged in a matrix. When an X electrode is selected and a voltage is applied between the selected X electrode and the corresponding Y electrode, the rising edge of this voltage changes with the electrostatic field between the selected X electrode and the corresponding Y electrode. If a finger, which is conductive, is placed near the selected X electrode, a capacitance is formed between the finger and the selected X electrode. Thus, the rising edge of the voltage between the X electrode, close to which the finger is placed, and its corresponding Y electrode varies in response to changes in the electrostatic field. By detecting the variations of the rising edge of the voltage, it can be determined what part of the flat-type input device is being controlled.
A flat-type input device of this type is mainly mounted in a keyboard apparatus of a personal computer. If a finger moves over a surface of the input device, for example, certain data for moving a cursor displayed on a screen is input.
Japanese Unexamined Patent Application Publication No. 2002-123363 discloses a small-sized portable apparatus in which the flat-type input device described above is mounted and a plurality of switching mechanisms are provided at a back side of the flat-type input device. When a specific area of this flat-type input device is pressed and the shape of the part of the flat-type input device is altered, the input device causes a corresponding one of the switching mechanisms to operate. In this input device, coordinate data following the moving path of the finger can be input by moving the finger over the screen of the flat-type input device. A switch signal can also be input by pressing one of the switch mechanisms.
However, in this apparatus, the flat-type input device and the switching mechanisms are used in combination; therefore, when a plurality of switching mechanisms are pressed simultaneously, it is difficult to determine which output signal deserves a higher priority among output signals supplied from the switching mechanisms.
The coordinate data is output by moving a finger over the screen of the flat-type input device, and a program indicated on the screen is selected. Afterwards, if a confirmation operation regarding the program is performed in response to a switch signal supplied from the switching mechanism located at the position related to the coordinate data, only the switching mechanism has to be properly operated. However, since the switching mechanisms are arranged on the same surface and operated independently from each other, a wrong switching mechanism may be pressed and unexpected operation may be performed when the confirmation operation regarding the program is attempted.